Postnatal growth, development and ultrasonic vocalization,of young Japanese field voles, Microtus montebelli

Abstract

Both postnatal growth and development of Japanese field voles, Microtus montebelli, were observed in a laboratory colony. Details of the developmental aspects of the life-history of this species are described focusing on behavioral development including ultrasonic vocalization, sexual dimorphism and the use of sigmoidal models of growth patterns. One purpose of the study was to provide a reliable basis for age-estimation of a wild population prior to conducting field investigations. The overall pattern of development of M. montebelli was similar to that of other Microtus species, particularly in their relatively rapid development. Young M. montebelli were found to vocalize intensively at an ultrasonic frequency of approximately 25 kHz until their eyes opened. The Gompertz equation was selected from three nonlinear growth models (Gompertz, logistic and von Bertalanffy), as it best described the curves of body mass increase and of four external lengths, and it best estimated maximum growth rates derived from the Gompertz equations fitted to actual rates during a linear growth phase. These features of the Gompertz equation seemed to be useful for analyzing growth patterns of wild voles. After 30 days, growth curves for each morphometric parameter diverged sexually, thus, weight-classes used for age estimation should differ between the sexes.